|
Shape-from-Silhouette with Two Mirrors and an Uncalibrated Camera
Keith Forbes, Fred Nicolls, Gerhard de Jager and Anthon Voigt
In Proceedings of the 9th European Conference on Computer Vision (ECCV), May 2006 | Abstract: Two planar mirrors are positioned to show five views of an object, and snapshots are captured from different viewpoints. We present closed form solutions for calculating the focal length, principal point, mirror and camera poses directly from the silhouette outlines of the object and its reflections. In the noisy case, these equations are used to form initial parameter estimates that are refined using iterative minimisation. The self-calibration allows the visual cones from each silhouette to be specified in a common reference frame so that the visual hull can be constructed. The proposed setup provides a simple method for creating 3D multimedia content that does not rely on specialised equipment. Experimental results demonstrate the reconstruction of a toy horse and a locust from real images. Synthetic images are used to quantify the sensitivity of the self-calibration to quantisation noise. In terms of the silhouette calibration ratio, degradation in silhouette quality has a greater effect on silhouette set consistency than computed calibration parameters. |
Creating Visual Hull Models Using Only Two Mirrors and an Uncalibrated Perspective Camera
Keith Forbes
Technical Report, 2005 | Abstract: We present closed form solutions for the focal length and pose of a camera and two mirrors that are computed directly from the silhouette outlines that appear in a single image. In the noisy case, we show how these equations can be used to form an initial parameter estimate that can be refined with a nonlinear iterative minimisation. This allows five-view visual hulls to be constructed from a single image. We show how these five-view visual hulls can be used to form initial estimates of the similarity transforms that relate multiple five-view silhouette sets of a rigid object in different poses. A nonlinear iterative minimisation is then used to refine the solution so that all silhouettes are specified in a common reference frame, and visual hulls can be constructed from an arbitrary number of silhouettes. Experimental results demonstrating the reconstruction of a toy horse are presented. |
Visual Hulls from Single Uncalibrated Snapshots Using Two Planar Mirrors
Keith Forbes, Anthon Voigt and Ndimi Bodika
In Proceedings of the Fifteenth Annual Symposium of the Pattern Recognition Association of South Africa (PRASA 2004), November 2004 Abstract: Two mirrors are used to create five views of an object: a view onto the object, two reflections and two reflections of reflections. The five views are captured in a single snapshot. Epipolar geometry of the object's five silhouettes is determined directly from the image without knowing the poses of the camera or the mirrors. The epipolar geometry provides constraints on the pose of each silhouette, allowing the pose of each silhouette to be computed in a common reference frame using only the silhouette outlines. Once the pose associated with each silhouette has been computed, a five-view visual hull of the object can be computed from the five silhouettes. By capturing several images of a rigid object in different poses, sets of five silhouettes can be combined into a single silhouette set in which the pose of each silhouette is known in a common reference frame. This allows visual hulls of an arbitrary number of views to be computed if more than one image is used. The method is applied to an ornamental cat, and experimental results are shown.
|
Using Silhouette Consistency Constraints to Build 3D Models
Keith Forbes, Anthon Voigt and Ndimi Bodika
In Proceedings of the Fourteenth Annual Symposium of the Pattern Recognition Association of South Africa (PRASA 2003), November 2003 | Abstract: The visual hull is the largest object that is consistent with a set of silhouette views of an actual object. The visual hull can be built from a set of silhouettes in which the viewpoint corresponding to each silhouette is known. We show how several sets corresponding to the same rigid object, each containing a small number of silhouettes, can be merged into a single large set. In order to do this, the relative pose between the sets must be computed so that each viewpoint can be specified in a common reference frame. We show how the poses can be computed by enforcing silhouette consistency constraints between the sets. The single merged silhouette set can then be used to build a visual hull model that is a closer approximation to the actual object than visual hulls built from any of the original sets. |
|
|
Last Updated on Monday, 02 February 2009 16:51 |
